Zed's Technical Writings

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Terminal Ballistics - A model to predict penetration depth

Posted by ZDP-189, in Technical, Uncategorized 08 December 2011 · 613 views

Summary
In this blog entry, I use data published by The Slingshot Channel to come up with a simplified formula to predict the depth of penetration of slingshot projectiles in ballistics gelatin. Gelatin has some initial resistance to penetration, but once you get over 20m/s (65fps), you can expect the the projectile to penetration its own...

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Comparing slingshot kinetic energy to common ball sports

Posted by ZDP-189, in General Info 08 December 2011 · 376 views

safety, kinetic energy

Summary

In this blog entry I consider how slingshots stack up against other other common human powered sports. I have selected a number of sports that involve a human flinging a ball, from golf to the shotput, from soccer to Jai-alai. Slingshots possess the least kinetic energy of all these sports. They aren't the fastest either....

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External Ballistics: Elevation/ Declination

Posted by ZDP-189, in Techniques, Technical 03 December 2011 · 659 views

external ballistics, elevation

I have previously touched on external ballistics and drop, but as my focus is target shooting and not hunting, I had not made a study of elevation. In this blog entry, I discuss:

Compensation for drop by aiming above the target
How a target that is higher or lower than the shooter affects the flight of the projectile

Please...

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Optics

Posted by ZDP-189, in Technical 02 December 2011 · 239 views

optics, safety glasses

Target shooting glasses

From my discussion thread: http://slingshotforu...ooting-glasses/

I have made some target shooting adjustable iris safety glasses.

Such devices are sometimes used for target shooting disciplines that require iron sights because they...

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Analysis of Shooting Form

Posted by ZDP-189, 24 November 2011 · 783 views

transitional ballistics

I have done some further analysis of Jörg's high speed video. It shows Tobias shooting full butterfly, a style which he mastered. I was impressed and intrigued by his form and chose to look at it in more detail.

Here he is at the start of the...

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Tapered Flatbands - Mechanism and Effect

Posted by ZDP-189, in Technical 19 November 2011 · 1,264 views

taper, bands, rubber

My good friend Jörg Sprave has been shooting very high speed video of the release phase of slingshots using the Phantom high speed camera. This shoots high quality video at 1,000 frames per second, allowing him to take calibrated measurements of distance travelled by a projectile over time. He published his data as a chart on his blog...

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Effect of temperature on rubber

Posted by ZDP-189, in Technical 14 November 2011 · 499 views

physics, bands, temperature

Why does rubber shoot faster on a hot day and slower on a cold day?

Natural rubber uses heat to contract. The more heat there is, the more it will contract. This can be shown as follows:
If you heat a band under load, it will contract.
Also, its resilience, which is the major input in band efficiency (the difference in the...

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Rubber is a maddeningly fascinating thing

Posted by ZDP-189, in Technical 07 November 2011 · 209 views

bands, taper

Aaron/mods, please don't feature this entry. it's just me thinking out loud to myself to ward off insanity.

Before you start reading, this is not a post full of answers; it's a post full of unanswered questions and conundrums.

We as a sport know surprisingly little about the physics of contracting rubber and there is not much...

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Stabilising non-round projectiles

Posted by ZDP-189, in Technical 30 October 2011 · 293 views

shuttlecock, pellet, dart

Summary

To summarise, don't try it; it's a fool's errand. Stick to smooth lead or steel round ball if you can.

Disclaimer

Don't do it. It's dangerous and there's no point as far as I can tell. If you ignore my warning and go ahead anyway, you'll...

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What's the optimal velocity?

Posted by ZDP-189, in Technical 29 October 2011 · 309 views

spin, drop, range, velocity

Intuitively, it may seem that we'd want to shoot a slingshot as fast as possible so you don't have to adjust for drop. That's really not what we want. We actually want to shoot reasonably fast. Not slow, but also not crazy fast.

At around 70m/s (230fps), at 10m (about 10 yards) a projectile drops 10cm (4 inches) on the way to...

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